“If he can do that for energy policy, just think what damage he would wreak on the economy. The solar subsidies inherited from Labour have been nothing short of a giant boondoggle.

“It’s crazy for politicians to try to pick scientific and commercial winners. It just ends up hiking energy bills paid by hard-pressed households and business, without making us more energy efficient.”

Mr Raab suggested the falling load factor had to “reflect variable weather and illustrates why solar is such an unreliable source”.

Last year ministers caused controversy last year by halving the rate of subsidy for a typical household from 43.3p per kilowatt hour of solar power to 21p per kilowatt hour, as the cost of the scheme grew.

A Department for Energy and Climate Change spokesman said that the panel's performance last year was poor because it was "not very sunny".

He said: "Small scale renewables make a valuable contribution to our energy mix but the increase in cost last year highlights why we were right to reign in the FITs scheme to make sure that the subsidy available reduces in tandem with rapidly falling technology costs.

"Last year was not a very sunny year, meaning performance of solar panels was lower, but this didn't in itself lead to any unnecessary subsidy as payment is only paid for electricity generated.

"The original budget for the FITs scheme has been exceeded but we agreed within Government that on the basis of the reforms we've made, including tight value for money controls, the scheme can continue to support these important clean energy technologies."